Modulating means



June 2, 1936. G. UsSr-:LMAN

- MODULATING MEANS Filed Sept. 20, 1932 4 Sheets-Sheet l INVENTOR GEORGEL. USSELMAN ATTORNEY BY MKM .Fume 2, 1936. G. L ussl-:LMAN 2,042,748

MODULATING MEANS Filed Sept. 20, 1932, 4 Sheets-Sheet 2 IIIllllllilllullhlilf vINVENTOR GEORGE L. USSELMAN *r l BY l AT1ORNEY June2, i936. G. l.. UssELMAN MODULATING MEANS 4 Sheets-Sheet 3 Filed sept.2o, 1952 INVENTOR GEORGE 1 ussELMAN BY f4 Wk ATTO'RNEY v m62? 1936! G.L.' ussELMAN 2,042,748

MODULATING MEANS Filed sept. 26, 1932 4 sheets-sheet 4 Patented June 2,1936 NETED STATES MODULATING MEANS George L. Usselman, Port Jefferson,N. Y., assignor to Radio Corporation of America, a corporation ofDelaware Application September 20, 1932, Serial o. 633,955

23 Claims.

This invention relates to signalling means and in particular to meanswhereby the characteristics of high frequency oscillations other thanamplitude are varied in accordance with signals to Vbe transmitted.

It has been found that ordinary amplitude modulated high frequencyoscillations in transmission from the sending stat-ion to the receivingstation are subject to what is known as fading effects. This is adecided disadvantage since it introduces drop-outs and errors in thesignal. Even where diversity receivers are used to receive the amplitudemodulated signals the effect of fading is of serious disadvantage.

I have found that if the high frequency oscillations are modulated inphase or in frequency in accordance with the signal to be transmittedthey are less subject to the effect of fading than amplitude modulatedwaves. The reason why phase or frequency modulated oscillations intransmission are subject to a less extent to fading effects thanoscillations modulated otherwise is that a greater amount of thetransmitter power is available for transmission. In other words,

15 a transmitter can operate at full output in phase or frequencymodulation while it is necessary to reduce the power output to aboutone-quarter for amplitude modulation. Assuming equal power output,reduction of fading may be slightly greater in phase or frequencymodulation than in other kinds of modulation.

In each of my United States applications, Serial No. 623,558, filed July20, 1932; Serial No. 616,026, filed June 3, 1932, Patent #2,036,165,dated March 31, 1936; Serial No. 602,487, filed April 1, 1932; andSerial No. 607,932, led April 28, 1932, Patent #2,036,164, dated March1, 1936, I have shown means for varying at signal frequency thecharacteristics other than the amplitude of a carrier frequency. In eachof these arrangements the carrier frequency is impressed substantiallycophasally on to the control grids of a pair oi thermionic tubes whichhave their `anodes connected in parallel to a common tank circuit andtheir internal impedances varied in phase opposition by the signal wave.In each of these arrangements the phase modulator stage comprises twotubes.

The present invention relates to an improved modulating means broadly ofthe type referred to above.

More in detail, this invention relates to an .improved modulating meanswherein the modulator S5-"stage comprises but a single tube and wherein(Cl. 179-171) i an efcient means is provided whereby variations in phaseor frequency of a carrier wave at signal frequency are accomplished.

The novel features of my invention have been pointed out withparticularity in the claims ap- 5 A pended hereto.

The nature of my invention and the operation thereof will be bestunderstood from the following detailed description thereof and therefromwhen read in connection with the drawings, lO

throughout which like reference numerals indicate like parts, and inwhich:

Figure 1 illustrates a specific embodiment of the invention; whileFigures 2, 3 and 4 illustrate modications of l5 the arrangement ofFigure 1.

A specific embodiment of my present invention is shown in Figure 1. Thistransmitter consists of the following stages and circuit. Asubstantially constant frequency oscillator A generates 20" the carrierfrequency and delivers it to a tuned tank circuit E comprising a tuningcapacity I and an inductance 2. The midtap of the inductance coil 2 ofthe tank circuit E is grounded for radio frequency by connecting thesame 25" through the by-pass condenser C1 to ground.

lTank circuits F and G are each inductively coupled to tank circuit Ethrough inductance coils I6 and I5 respectively and variably inductivelyrelated to inductance 2 of tank circuit E. Tank 30v circuit F iscomposed of inductance coil I6, Xed condenser I4, resistor I2, andvariable tuning capacity I8; while tank circuit G is composed of coilI5, Xed condenser I3, resistor II, and variable tuning capacity I'I.Tank circuit F is 85 grounded at one end for radio frequencyoscillations by a lead connected between condenser I4 and resistor I2through by-pass condenser 21 to the grounded filament lead FL. Tankcircuit G is grounded for radio frequency oscillations 40 by the samelead connected between condenser I3 and resistor II through by-passcondenser 21 to the grounded filament lead FL. These points on each tankcircuit are also connected by Way of lead 32 to the positive terminal ofthe power 45` supply 26.

Tubes I and J are the amplitude modulator tubes. 'I'he anode electrodeIll of tube I is connected to the tank circuit F at a point betweenresistor I2 and variable condenser I8, while the 50 anode 9 of tube J isconnected to the tank circuit G at a point between resistor II andvariable condenser I'I. Control grids 'I and 8 of tubes J and I areconnected in phase opposition to the secondary winding i9 of transformerT1. 55

Vlead FL, as shown.

Parasitic prevention resistors 3 and 4 are inserted in the connectionsbetween the terminals of the winding 2 and the control grids 1 and 8respectively. These resistors are also grounded at the ends adjacentwinding i9 for radio frequency by connecting said ends through by-passcondensers 5 and 6 to the grounded lament The midpoint of the secondarywinding I3 of transformer T1 is connected by lead GB to. a point onthepotentiometer P1 connected in parallel with a portion of the source ofdirect current 26. In this manner negative bias of the desired potentialmay., be applied constantly to the control electrodes "i' and 8 of tubesJ and I. The primary winding of transformer T1 is connected to a sourceof signal frequency B as shown. Cathodes 2G and 2l of tubes I and J areconnected t6 the power supply circuit FL, which is in turn connectedwith a portion of source 26, as shown.v

One end of phase retarding element L is connected to tank circuit F at apoint between inductance coil i6 and variable condenser lla, andlikewise one end of phase advancing element M is connected to tankcircuit G at a point between inductance coil i 5 and variable condenserIl. The other ends of both phase shifting elements L and M are connectedtogether and are also connected through blocking condenser 22 to thecontrol grid 24 cf thermionic modulator tube K. Tube Kv and tank circuitH comprising tuning capacity 3i and inductance 32 is the phase modulatorstage. Control grid 24 of tube K is supplied With steady negative bias4from the power source 26, through the resistor 23 and lead 33, which isconnected to a` movable point on potentiometer resistance P. The lowerend of resistor 23 is grounded for radio frequency currents through theby-pass condenser 28 as shown. The anode 25 of tube K is connected, asshown, to the top of tank circuit H. Charging potential is supplied toanode 25 from source 26 through theinduotance coil 32 of tank circuitHand lead 34. The lower end of tank circuit H is grounded for radiofrequency oscillations.. through the by-pass condenser 29, as shown inFigure 1.

Tube K is shown as the screen grid type but a three element tube may beused by providing grid neutralizing arrangements. Charging potential forthe screen grid electrode 35 of tube Kis supplied by way of lead 36 froma potentiometer P2 connected in parallel with direct current, source 26.Any radio frequency oscillations reaching the screen grid electrode 35are shunted around source 26 by by-pass condenser The tank circuit H'isconnected to the stage C through a line including blocking condenser 36.Stage C may contain amplitude limiters, frequency multipliers andamplifiers, or any combination of the three. The output stage of C isconnected toa load circuit, which, in this v cillatonAby,thevariablecondensers I8'and I 'I respectively. Note also that the coupling betweeninductance coils i6 and I5 and inductance 2 of tank circuit E isadjusted to a value such that energy of equal amplitude is impressed onto the tank circuits f and g.

Now, if there -is no signal present, the excitation energies reachingthe control grid 24 of tube K from source A by way of tank circuits Fand G will be vof equal amplitude. assumed that the impedances'of phaseshifting elements L and M to the high frequency oscillations from A areequal, which they should be.

The phase of the carrier energies reaching 24 fromA tank circuits F andG will be shifted in opposite' directions relative to an average phasevalue by the phase shifting elements L and M. When there is no signalthe resultant excitation energy applied to the control electrode 24 willhave a constant phase angle which will be half way between the extremelimits of the modulating angle. Tank circuit H may be tuned by capacity3l to the frequency of the source A or to a harmonic of said frequency,in which case the phase modulator stage K will either ampify or multiplythe oscillations from A. This carrier energy in tank circuit H then maybe either amplitude limited, or frequency multiplied, or amplified, orany one or more oflsaid operations may be carried out in stage C beforethe energy is radiated by antenna D.

Now, if We assume that signal frequency is being sent out from source B,it will be transmitted through' transformer T1 to the grids 'I' and 8 oftubes J and I. The signal from B may consist of alternating voltages ofvariable ami lower than the alternating current resistance of Y tube I.Now you will note from Figure 1 that the anode to cathode impedance oftube J is, in effect, connected in parallel with resistor Il of tankcircuit G, while the anode to cathode impedance of tube I is, in effect,connected in parallel with resistor l2 of tank circuit F. Since theinternal impedance of tube J has been reduced by the signal and also theanode to cathode impedance of tube I has been increased by the signal,the total resistance in tank circuit G is consequently reduced while thetotal resistance in tank circuit F is increased. This causes an increasein the amplitude of the car-- rier voltage in tank circuit G and acorresponding decrease in the amplitude of the carrier voltage in tankcircuit F.

The carrier energy reaching the grid 24 of the tube K from the tankcircuit G will be increased a certain amount while the carrier energyreaching grid 24 from tank circuit F will be decreased by the sameamount. Taking into account the phase shift of thel carrier voltagesdelivered by circuits `G and F, through the phase shifting elements Mand L, the resultant excitation voltage amplitude is constant but thephase angle of the resultant has shifted. In this case it has beenadvanced in phase. It can be shown by vector analysis that, as tubes Jand I are differentially amplitude modulated, the total excitationenergy reaching grid 24 is constant rbut of changing phase angle. Thefrequency of this phase modu- This follows if it is lation will be thesignal frequency and the degree of phase modulation will be proportionalto the intensity or amplitude of the signal. The limit of the amount ofphase modulation possible can :be set by adjusting the capacity ofcondenser M and by adjusting the inductance of coil L. Thecharacteristics of the resultant excitation on grid 24 are transmittedon through the various stages, in which the phase modulated carrier maybe namplified or multiplied in frequency, or both.

of phase modulation is increased in thesame ratio.

In practice the phase shifting means L and M may each comprise avariable capacity and inductance in series, as illustrated in Figure 2,

wherein the improved phase or frequency modulator is otherwise the sameas the arrangement of Figure 1. Moreover, the phase shifting elements Land M of Figures 1 and 2 may, where desired,

, be replaced by lines or conductors of diiferent electrical length toobtain the desired phase shift. 'Ihe use of such lines of diiferentelectrical length has been disclosed by me heretofore in my UnitedStates application Serial No. 607,932, filed April 28, 1932, Patent#2,036,164, dated March 31, 1936.

The operation of the arrangement of Figure 2 is the same as thearrangement of Figure 1.

In the arrangement of Figure 3 the phase shifting elements L and M havebeen replaced by ohmic resistances R2 and R3 respectively. Theseresistances do not cause a phase shift in the carrier frequency energyapplied to the control electrode 24 by way of tank circuits F and G. Inorder to obtain the necessary phase shift in the carrier frequencyenergy applied by way of tank circuit F and G, I tune one of thecircuits to a frequency slightly above resonance, that is, above thefrequency of the oscillations introduced from A by Way of tank circuit Eto tank circuits F and G, and detune the other circuit, that is, tunethe other circuit to a point slightly below resonance, or below thefrequency of the oscillations reaching the circuits F and G, from A byWay of tank circuit E. More specifically, the tank circuit F may betuned to a frequency f-l-fl where f is the resonant frequency, orfrequency of the tank circuit E, and f1 is in increment suiiicient toobtain the desired phase shift of the carrier energy. The tank circuit Gmay be tuned to a frequency f-fi. Here again is the frequency to whichthe tank circuit E is tuned and f1 is in increment in frequency sufcientto apply to the carrier frequency leaving the tank circuit G the desiredphase shift. The total impedance of circuits F fand G will depend here,as in Figure l, on the impedance between the anodes and cathodes oftubes I and J. 'Ihis impedance in turn depends on the signal potentialapplied to I and J from T1.

The modification shown in Figure 3 is otherwise similar to thearrangement of Figure 1. Moreover, the operation of the arrangement ofFigure 3 is the same as the operation of the arrangement of Figure 1,except as otherwise hereinbefore noted. The phase retarded oscillationsof tank circuit F are applied by way of ohmic resistance R2 to thecontrol electrode 24 of tube K, while the phase advanced oscillations oftank circuit G are applied by way of ohmic resistance R3 to the controlelectrode 24 of phase or frequency modulator K.

In all of the modifications shown above the tank circuit H may be tunedeither to the fundamental frequency, that is, to the frequency of theoscillations from A, or it may be tuned to any harmonic of the frequencyof the oscillations from A.

Where desired the tank circuits F and G may be coupled to'tank circuit Ethrough capacities,

-as indicated in Figure 4, rather than by way of inductive coupling, asshown in Figure 1, or the tank circuits F and G may be coupled to tankcircuit E capacitively and inductively, as shown in Figures 1 and 4.

'Ihe capacities 40, 4| may be fixed and connected, as shown, by variabletaps to the inductances 2 and I6 and l5 or the capacities may beVariable and connected, as shown, to movable points or to xed points onsaid inductances.

The arrangement of Figure 4 is otherwise the same as the arrangement ofFigure 1. Moreover, the operation of the device of Figure 4 is so likethe operation of the arrangement of Figure 1 that it is thoughtunnecessary to repeat said operation at this point.

Having thus describedv my invention and the operation thereof, what Iclaim is:

l. The combination of a source of high frequency oscillations, athermionic modulator tube, a pair of tank circuits coupled to saidsource, a connection between each of said tank circuits and said tube, afixed resistance and a variable resistance in each of said tankcircuits, and means for varying said variable resistances at signalfrequency to produce phase modulation of the oscillations from saidsource.

2. The combination of a source of high frequency oscillations and athermionic modulator tube, of a pair of tank circuits coupled to saidsource, means for tuning each tank circuit to a diiferent frequency, avariable resistance in each of said tank circuits, impedances of similarcharacter connecting each tank circuit to the control electrode of saidtu ,and circuits for varying said resistances at signal frequency.

3. Means for modulating the phase of oscillations from a source of highfrequency oscillations comprising, a thermionic modulator tube, a pairof tuned tank circuits coupled to said source of oscillations, a fixedresistance and a variable resistance in parallel in each of said tankcircuits, phase shifting impedances connecting said tank circuits to theinput electrode of said tube, and means for varying said variableresistances at signal frequency.

4. Phase modulated wave producing means to be used with a source of highfrequency oscillations comprising, a thermionic tube, a pair of tankcircuits interposed between said source of high frequency oscillationsand the control electrode of said tube, a resistance in each of saidtank circuits, a thermionic impedance connected in parallel with each ofsaid resistances and means ffThe-combination of a'source of high'frequency.v oscillations, a tank circuitA connected thereto, athermionictube, a pair of tank circuits symmetrically coupled to said source ofhigh i frequency oscillations, a pair of thermionic tubes,

means for connecting the internal impedance of onelof said pair of tubesin one Vof said tank circuits, means for connecting the internalimpedanceV of the other of said tubes in the other `'of said'pair oftank circuits, `phase shifting elef ments of different charactersticsfor coupling each tankcircuit to the control electrode of said firstnamed thermionic tube, and a source of signal potentials coupled to anelectrode in each of saidfpair of thermionic tubes. f

71 Phasemodulating means comprising, a thermionic tubeadapted to repeathighfrequency oscillations,'fa"pair:cftank circuits tuned to differentfrequencies'an'd `responsive to high frequency oscillations, resistancesconnecting each of said tank circuits to the input electrodes of saidtube, a fixed impedance in each of said tank circuits,-a

variableiimpedance connected in parallel With each of said fixedimpedances, and means for varying oppositely the impedances of saidvariable impedances at signal frequency.

8. Signal `modulating means comprising, a thermionic tube adapted torepeat high'frequency oscillations, a pair of tank circuits responsiveto highV frequency oscillations, means for .tuning said.

tank 'circuits to different frequencies, impedances connecting each ofsaid tank circuits tothe input electrodes 'of said tube, a'pair ofthermionic tubes, `means :for connecting the internal impedance of oneof said'tube in Vone of said tankv circuits and; of the other of said"tubes in.. the other/of said tank circuits, and means forvaryingfthe-impedances of .said tubes atsignal frequency.

9: vrMeans for modulating high frequency 'oscillati-ons comprising;l athermionicimodulatoigi a pair of tuned tankcircuits, means forimpressinghigh frequency oscillations symmetrically on said tank circuits,impedances connecting each of said tankicircuits to the controlelectrode of said tube, a pair of thermionic tubes, means for connectingthe impedance of each of said thermionic vtubes in seriesl with adifferent one of said tank circuits,

andimeans for varying inr phase opposition at signal-'frequency theimpedances of said tubes.

10. A phase or frequency modulator comprising,"a thermionic modulatortube, a source of high frequency oscillations, a'pair vof tank circuitssymmetrically coupled to said high frequency source '5 ofoscillations,phase shifting means .interposed 11. A phase or frequency modulatorcom'- prising, a thermionic modulator tube, a source of high frequencyoscillations, a tank circuit connectedtheretdav pair of .tank circuitssymmetrically coupled to said first named tank circuit, impedancesinterposed between each of said pair of tank circuitsand the controlelectrode of said thermionic 'modulaton an impedance inseriesc with eachof said tank circuits, a pair of thermii onic-tubes, means vforconnecting the anode'to cathode impedance of one of said tubes inparallel With the impedance in oneeof said tank circuitsY andthe 'anodeto cathode impedance Vof the other 0f said tubes infparallel with theimpedance of-f the other o'f said tankcircuits, a source of signalpotentials, means for applying signal potentials from said source to thecontrol electrodes of said tubes in phase opposition, and means fortuning-vv each of said pair of tank circuits to a different fre--vquency.

12. Transmitting means comprising, a source of high frequencyoscillations, a source of signal potentials, a thermionic modulator tubehavingv a Work circuit connected With the output ele'e-- trodes thereof,a pair of tank circuits, capacitive means for coupling said tankCircuits Vsub-- stantially cophasally to the output of said highfrequency oscillator, a pair of thermionic tubes, means for connectingthe anode to cathode impedance of one of said tubes in'series-With one-vzofff of Vsaid tank circuits, means for connecting the anode to cathodeimpedance of theother ofsaid tubes in series With the other of said tankcircuits, phase advancing means connecting lone of said tank circuits tothe control electrodeof said thermionic modulator tube, phase retard--ing means connecting the other of said tank circuits tothe controlelectrode of said thermionic modulator tube, and means for oonnectnginlphase opposition the control electrodes of said pair of tubes to saidsource of signal potentials.

13. A circuit for modulating the phase of carrier frequency oscillationscomprising, a tuned tank circuit adapted to be energized by carrier'frequency oscillations, a modulator tube having an output circuit, acontrol electrode and a cathode, a pair of tank circuits, eachcomprising an inductance and a capacity in Aseries with a' resistance, acoupling between each of said pair of tank circuits and said tuned tankcircuit, impedances connecting each of said pair offtankcircuits to thecontrol electrode of said modulator tube, a pair of thermionic tubes,each having anode, cathode and control grid, a circuit for connectingthe anode to cathode impedance of one of said tubes in parallel With theresist-*- ance in one of said tank circuits, a circuit for connectingthe anode and cathode impedance of the other of said tubes in parallelWith the-resistance in the other of said tank circuits-and a source ofmodulating potentials connected in phase opposition to the control gridsof said tubes.

14. A phase modulator comprising, a high frequency oscillator, athermionic tube having" input electrodes, a pair of tank circuitscoupledz to said oscillator, means for tuning said tank circuits to aharmonic of the frequency of saidv oscillator, a phase advancingreactance connecting one` tank circuit tothe input electrodes of" saidtube, a phase retarding reactance connecting the other tank circuit tothe input electrodes.. of said tube whereby a relative phase shiftisproduced in the oscillations transferred from. said oscillator by Way ofsaid tank circuits to.v the input. electrodes of said tube, an impedanceVariable at signal frequency in each tankA circuit,A and means connectedwith said impedances to'.y vary the Values thereof alternately atsignaly frequency to produce variations in the intensity'.

of oscillations transferred to the input electrodes f of said tube byWay of the respective tank circuits.

15. Phase modulating means comprising, a thermionic tube adapted torepeat high frequency oscillations, said tube having input electrodes, apair of tank circuits each including series reactances, a source of highfrequency oscillations, reactances coupling said source of highfrequency oscillations to said reactances in said -tank circuits, phaseshifting elements connecting each of said tank circuits to the inputelectrodes of said tube, said aforesaid reactances being of a natureto,transfer substantially in-phase oscillations to said phase shiftingelements, a variable impedance in each of said tank circuits, and acircuit for Varying said impedances at signal frequency, to thereby Varythe amount of oscillatory energy reaching the input electrodes of saidtubes by way of said respective tank circuits and said phase shiftingelements.

16. The combination of a work circuit, a source of high frequencyoscillations, a symmetrically grounded tank circuit coupled to saidsource, an asymmetric translating device connected to said work circuit,a pair of circuits tuned to different frequencies and connected tosaidtranslating device, Variable couplings between said tank circuits andsaid source of high frequency oscillations, said tuned circuits andcouplings normally transferring phase displaced oscillations to saidtranslating device to produce therein resultant oscillations, and meansfor varying the response of said tuned circuits to oscillationstransferred thereto from said source of high frequency oscillationsalternately at signal frequency to thereby vary the phase of theresultant oscillations in said translating device.

17. The combination of a high frequency oscillator, 'a thermionicrepeater having input electrodes and output electrodes, a work circuitcoupled to the output electrodes of said repeater, a

pair of tank circuits tuned to different frequencies, said tank circuitsbeing symmetrically coupled to said source of high frequencyoscillations, impedances of like character coupling said tank circuitsto the input electrodes of said thermionic repeater, and means forvarying the impedances of said tank circuits alternately at signalfrequency to thereby produce relative phase shifts in the oscillationstransferred by said tuned circuits from said oscillator to saidrepeater.

18. The combination as recited in claim 16 in which a frequencymultiplier is interposed between said work circuit and said asymmetrictranslating device.

19. The combination as recited in claim 17 in which an amplitude limiterand frequency multiplier are interposed between said work circuit andsaid thermionic repeater.

20. A device as recited in claim 17 in which a circuit includingreactances tuned to a harmonic of the frequency at which said highfrequency oscillator operates is interposed between the outputelectrodes of said thermionic repeater and said work circuit.

21. A signaling system comprising a phase modulating means as recited inclaim 15 in which said thermionic tube has output electrodes in which acircuit tuned to a harmonic of the frequency of the oscillations of saidhigh frequency source is connected to said output electrodes.

22. A phase modulating means as recited in claim 15 wherein said phaseshifting elements each comprise series tuned reactances.

23. Means for modulating high frequency oscillations as recited in claim9 wherein said pair of tuned tank circuits are tuned to a harmonic ofthe high frequency oscillations to be modulated and wherein saidimpedances each comprise series tuned reactances.

GEORGE L. USSELMAN.

